Imaging and optical sensing devices are widely used in both commercial and military applications. In traditional configurations of focused optical imaging or sensing systems, a sensor array is located in the image plane and oriented perpendicular to the optical axis. This configuration is necessary to keep the image in focus across the entire active area of the imaging detector; however this configuration makes the system retro-reflective. As a result, any light not absorbed by the sensor (e.g., a camera or focal plane array sensor) is reflected and imaged directly back to the source along the same optical path as the incident light (i.e., retro-reflected).
Optical augmentation (OA) systems use this property of retro-reflection to detect hidden optical systems. For example, an OA interrogator uses an active light source to sweep through an environment illuminating any target optical devices, and retro-reflection leads the “cat's eye” effect, which allows any illuminated target optical systems to be identified, located and characterized. Even though the location of the interrogator may be easily determined, by the very fact that the target optical system observes the interrogation beam, its location is revealed. In addition, the OA system may determine some information about the technical specifications of the target optical system from the nature of the retro-reflections.